Heat treatment of structural sections



Nov. 14, 1967 MCNITT ET AL 3,352,724

HEAT TREATMENT OF STRUCTURAL SECTIONS Filed June 14, I965 2 Sheets-Sheet1 INVENTORS. LEWIS F. M NITT a EDMUND MELGUN 74am 5. MW

ATTORNEY Nov. 14, 1967 F. MGNITT ET AL 3,352,724

HEAT TREATMENT OF STRUCTURAL SECTIONS Filed June 14, 1965 r 2Sheets-Sheet 2 FIG. 5 "W; 123

H COMPRESSION STRESS HEAT TREATED FIG. 6

HEAT TREATED bi TENSION INVENTORSQ STRESS LEWIS E MCNITT a B EDMUND L.MELGUN Y 7WS/Waqnw ATTORNEY United States Patent 3,352,724 HEATTREATMENT OF STRUCTURAL SECTIONS Lewis F. McNitt, Bay Village, andEdmund L. Melgun,

Cleveland, Ohio, assignors to Midland-Ross Corporation, Cleveland, Ohio,a corporation of Ohio Filed June 14, 1965, Ser. No. 463,652 2 Claims.(Cl. 148--144) This invention relates to heat treatment of structuralsections and, more particularly, to selective heat treatment of areas ofthe sections that may be subjected to excessive bending type loads alongtheir length; the treatment leaving the structural section without anysignificant distortion.

Structural shapes are generally symmetrical about 1ongitudinai axes andmay take the form of a channel, I beam, wide-flanged beams, or rolledsections. Each of these shapes can be advantageously subjected to thehereinafter described heat treatment and to only the areas or sectionssubjected to excessive loading of axial or column type and/or bending.The structural shapes are generally used in frames of trucks, as floorjoists, roof supports, columns, and often where either axial or bendingtype loads are imposed. As an example, in the trucking industry, achannel shaped member is used in the frame for side rails as loadsupporting beams, as well as in trailer frames. Also, such members mightbe used for support of railroad cars requiring resistance to bendingtype loads.

The heat treatment method of this invention gives the sections used inthe aforesaid example an increase in strength in substantial amounts inthe treated areas without any further structural buildup that otherwisewould be required. The proposed heat treatment is by means of inductionheating apparatus, the electrodes designed to conform to the shape orform of the structure to be treated. By way of example, the method ofthis invention will be described in connection with a channel structureused in a frame of a truck, as in a cement carrier.

The method, in general, is one of selective heating, initiallypreparatory heating of the center and the outer flanges of a channelmember, followed by high heat effecting hardening, then a water quenchand a drawing or tempering of that portion of a channel which it isdesired to improve over its basic physical strength characteristics.Temperatures used depend somewhat upon the quality of the structuralsteel and its thickness, however, all steels can' benefit in an increaseof strength. Steel utilized in frames for trucks usually is an alloyedmaterial standardized type including those chemical elements whichcontribute to grain refinement and hardenability. Such steels arecapable of being increased in hardenability and strength considerably,by about at least 100% or more over its basic hardness and strength, andwithout noticeable distortion when subjected to the herein describedtreatment. A substantial increase is particularly advantageous in truckframes for it provides greater additional strength and toughness inareas where most needed and without much increase in cost. The method ofraising the impact strength of truck or trailer frame steels will bemore thoroughly described in the following specification taken inconnection with the accompanying drawings, where:

FIGURE 1 represents a form of truck and its supporting frame;

FIGURE 2 shows a section of the truck frame side member of FIGURE 1 anda form of induction heating device followed by a water cooling means;

FIGURE 3 is a cross section of the truck frame side member of FIGURE 1taken across line 3-3;

FIGURE 4 is a sectional detail of FIGURE 2 along the line 44 thereof,showing the position of the induc tion heater unit relative the frameside member;

FIGURE 5 is a further sectional detail of FIGURE 2 along line 5-5showing the following water quenching means; and

FIGURE 6 graphically represents the selective stress improvement,particularly in the highly stressed flange sections.

By way of example, there is shown in FIGURE 1 a standard cement mixertruck 10, its superstructure being supported on a frame having siderails 11 in the form of channels. The truck frame itself is supported bywheels 14 in front and 15 in the rear. Generally, as assembled, thetruck frame comprises two identical, equispaced, longitudinallyextending channel members 11 each having a cross section as shown inFIGURE 3. A common dimension of a side channel member 11 is about 25feet long, 9.5 inches deep with flange width of about 3 inches andhaving a thickness of about .250 inch. The side channel members 11 areinterconnected by cross members (not shown) to provide for transverserigidness as well as for further support of the trucks superstructure.

As seen in FIGURE 1, there is a substantial length of a side member 11that is not directly supported, the length being that between the frontand rear wheels. It is in this area where additional impact or bendresisting strength is needed. Advantageously, this additional strengthcan be achieved by selective heat treatment of the side rail 11,particularly of the flange area of each side channel member 11, leavingthe web section unhardened for subsequent utilization during buildup,the drilling being done with ordinary tools. The method of selectivelyheat treating a channel member having the dimensions given hereincontemplates full heat treatment of the flanges and adjacent area partway down the web only to a hardening value of from an initial hardnessof from 60,000-80,000 p.s.i. to about 135,000-150,000 p.s.i. The heatingand quenching in the process is done on a continuous basis and asrapidly as the desired temperatures in the material are reached.Generally, it was found that truck frame steels when subjected totemperatures of about 1650 F., then quenched and subsequently drawn andquenched would give a yield strength increase of from about 60,-000-80,000 p.s.i. to about and more than 135,000 to about 150,000 p.s.i.This substantial improvement in strength is imposed only on the flangedor selected portions of the side member yet leaving the web soft, andthe channel is, advantageously, not effected with any significantdistortion. The treatment yields a highly strengthend and toughened sidechannel member at a slight additional cost.

One form of an induction heating electrode 17 (not a subject of thisinvention) may be as generally indicated in FIGURE 2 where the highestconcentration of heat i had about the flanges of the channel 11 whilethe web section itself is subjected to considerably less heat. Theinduction unit or electrode 17 is formed of two sections 18 and 19. Thefirst section 18 initially preheats the entire channel 11, the secondsection 19 follows up with substantially higher temperatures only aboutthe flanged sections. More specifically, the electrode 17 is soadvantageously devised that it preheats the web area of the channelmember 11 initially by the prior electrode section 18 to about 400 to600 F. and the flanges to about 900 F. then, also selectively, thefollowing electrode 19 raises the temperature to about 1600l700 F. toharden only the flanges and adjacent web portions. The low and highheating is followed by an immediate water quench 20. After thequenching, the induction unit 17 again is passed over only the highlyheated flange and web areas at a range to permit drawing temperatures of800 F. to 1200 F.

This method yields a highly desirable increase in flange hardness andstrength yet an insignificant distortion of the and pressure of thewater quench can be readily determined to quickly yield the lowtemperatures required prior to drawing. 7

For uniform treatment, it is desirable that the'electrodes 18, 19 of theinductor 17 be spaced and maintained spaced at a most effective distancefrom the channel or rail surface being treated, in this example, thedesirable distance being about from .1875 inch to .250 inch. Thisuniformity of spacing is shown in FIGURE 4. The highly heated flangesections of the channel 11 are desirably quicklychilled bythe'immediately following quench 20 comprising opposite inwardlyperforated sections 22, 23 having a desirable number of outlets on theinner or channel side and conforming in shape to about the channel 11sides. While.

the cooling is effected primarily on the sides of the channel or on theends, the water quickly overflows over the entire cross section. The websection being originally heated to only about 400600 F. although waterquenched is not structurally disturbed thus preventing subsequentdistortion. The quench water is readily brought.

in to the quench head sections 22, 23 through external supply sources25, 26. Again, after the drawing of the flanges of the member 11 at atemperature of about 900 F.1200 F., the side channel member is quenched.This was found to be necessary to control any tendency of'the channel tolongitudinal distortion.

As shown in FIGURE 6, the original channel or member 11 upon treatmentby the methods described and as 4 operation followed by an immediatequenching. With the draw temperature being about 900 F the yieldstrength was raised to at least about 130,000 p.s.i. It was found,however, when the draw temperature was further increased to about 1000F., the yield strength was lowered somewhat to about 127,000 p.s.i. Theelongation and distortion of the member remained within tolerablelimits.

The method is advantageous in that it reduces costs where it is desiredto increase the strength of steel mem bers of common manufacture overspecial steels to offset higher loads; the treated members permitseveral load carrying capacities on the same wheel base; the dimensionalstability is excellent, the web portion is left soft, thus simplifyingthe drilling of holes; a single type of steel can be kept in inventoryfrom which variable strength frames can be built; fabricating equipmentneed not be extensivei more load can be carried for a given weight, etc.

What is claimed is: I

1. The method of heat treating a low carbon steel channel formcomprising, preheating the web area to a temperature of not lower thanabout 400 F. and the flange sections to about 900 F. unaffecting amolecular change therein, substantially immediately thereafter heatingthe flanged portions and desired areathereabout only to a temperature offrom 1600l700 F., substantially immediately applying a quench to causehardening sufficient to form a martensitic structure in the said area,thereafter again applying heat at a temperature of about 900 F.

. to the said desired higher heated area to draw the temper shownintermediately graphically assumes the greatest allowable stressincrease in the flange area where required while the web area is hardlyaltered. The web area is thus left relatively soft and unhardened foreasy drilling or punching out for necessary cross member support andother attachments While the load bearing flanges are considerablyincreased in their capacity to carry higher stresses.

EXAMPLE By way of a specific example, a .25-inch-thick plate of steelknown in the trade a J alloy S with a molybdenum content of about .26%and having a yield strength of about 60,000 p.s.i. was cut and formedinto a member shaped as a channel having 9.5 inches width (overall) with3-inch flanges. The channel member was subjected to the describedmethod, the inductor 17 element 18 initially preheating the channelmember to about 400 F. in the web section and to about 900 F. about theflanges, and immediately thereafter element 19 raises only the flangedportions to about 1650 F. (3 inches in width and about 2 inches into theweb). Immediately upon the high heating, the flange portions arequenched by a water spray at a pressure of about 8 p.s.i. The inductor17 then again is passed over the channel flanges at about 900 F. in adrawing of said flanges, and thereafter again quenching.

2. 'The method of treating a symmetrical longitudinally extending lowcarbon steel channel section of about .25- in-ch thickness and having atleast a trace of molybdenum to effect a hardening of outer portions onlyleaving the inbetween portion substantially unaffected comprising,preheating. the entire cross-sectional area to a temperature of notlower than about 400 F. and not above about 900 F. unalfecting amolecular change therein, then substantially immediately thereafterhighly heating the desired outer flange portions only leaving the webportion unaffected to temperatures of from 1600 -l700 F., substantiallyimmediately water quenching the heated portions to effect hardeningsufiicient to form a martensitic structure in the said area, thereafteragain applying heat at a substantially lower temperature in the range ofabout 800-1200 F. to draw the temper of said outer portions, andthereafter again water quenching.

References Cited UNITED STATES PATENTS 2,207,758 5/1940 Denneen et al.148 l X 2,686,460 8/1954 Bridge et a1 148-150 X 3,121,780 2/1964 Muchaet al 2664 X 3,148,093 9/1964 Williams et al. 148-145 X 3,251,588 5/1966French 2664 X 3,278,349 10/ 1966 Husebyet al 1484-146 X I 3,294,59712/1966 Kuchera a 148-143 FOREIGN PATENTS 1 237,227 8/ 1945 Switzerland.

CHARLES N. LOVELL, Primary Examiner,

1. THE METHOD OF HEAT TREATING A LOW CARBON STEEL CHANNEL FORMCOMPRISING, PREHEATING THE WEB AREA TO A TEMPERATURE OF NOT LOWER THANABOUT 400*F. AND THE FLANGE SECTIONS TO ABOUT 900*F. UNAFFECTING AMOLECULAR CHANGE THEREIN, SUBSTANTIALLY IMMEDIATELY THEREAFTER HEATINGTHE FLANGED PORTIONS AND DESIRED AREA THEREABOUT ONLY TO A TEMPERATUREOF FROM 1600-1700*F. SUBSTANTIALLY IMMEDIATELY APPLYING A QUENCH TOCAUSE HARDENING SUFFICIENT TO FORM A MARTENSITIC STRUCTURE IN THE SAIDAREA, THEREAFTER AGAIN APPLYING HEAT AT A TEMPERATURE OF ABOUT 900*F. TOTHE SAID DESIRED HIGHER HEATED AREA TO DRAW THE TEMPER OF SAID FLANGES,AND THEREAFTER AGAIN QUENCHING.